Sliding members, such as pistons and valve-system component parts making engines, have been subjected to various surface treatments in order to suppress wear or seizure. In particular, an amorphous carbon film, a so-called diamond-like carbon film (hereinafter abbreviated to as “DLC” wherever appropriate), has been used widely as a film for enhancing the sliding members' sliding ability, because it is good in terms of mechanical characteristics, such as wear resistance and solid lubricating property. Moreover, various studies have been done on the film compositions of amorphous carbon film and the processes for producing the same in order to furthermore upgrade the mechanical characteristics of amorphous carbon film. For example, Japanese Unexamined Patent Publication (KOKAI) No. 3-240, 957 discloses an amorphous carbon film containing silicon, and a process for producing the same. Moreover, Japanese Unexamined Patent Publication (KOKAI) No. 7-54,150 discloses an amorphous carbon film containing silicon and nitrogen, and a process for producing the same.
For example, automotive engines' sliding parts might be exposed to considerably high pressures. Accordingly, an amorphous carbon film is required to exhibit high wear resistance. However, in Japanese Unexamined Patent Publication (KOKAI) No. 3-240, 957 and Japanese Unexamined Patent Publication (KOKAI) No. 7-54,150, the amorphous carbon films are only examined for the wear characteristics under such low-load sliding conditions as from 5 to 6 N. Moreover, the conventional amorphous carbon films disclosed in the two publications exhibited a wear amount of from 0.2 to 0.3 μm, respectively, even under the low-load sliding conditions. That is, the conventional amorphous carbon films exhibited a large wear amount, respectively, despite the low-load sliding conditions. Thus, it is not possible to say that the conventional amorphous carbon films' wear resistance is satisfactory.
Moreover, from the viewpoint of durability, there might arise cases where it is desirable to thicken the film thickness of amorphous carbon film. Note herein that the conventional amorphous carbon films, disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 3-240,957 and Japanese Unexamined Patent Publication (KOKAI) No. 7-54,150, exhibited a high hardness, respectively. A high-hardness amorphous carbon film usually exhibits a high elastic modulus. Accordingly, when thickening the film thickness of high-hardness amorphous film, the internal stress of high-hardness amorphous carbon film enlarges so that the thickened high-hardness amorphous carbon film is likely to peel from a substrate or even break up. Consequently, it has been difficult to thicken the conventional amorphous carbon films to a thickness of 10 μm or more.